Logs in a user. Returns 0 on failure. If $username is 'anonymous' then it will try to login as 'ftp' with no password. If $become is defined then it will try to change ownership of the process to the uid/gid of the logged in user. BEWARE of the consequences of using $become. login() also sets the uid, gid, home, gids, home_path, and chdir to the users'.

Opens a file with IO::File. Params are passed to open() of IO::File. It returns the file handle on success or undef on failure. This could be technically be used for any sort of open operation. See IO::File's open method.